In firearms of these types, breech bolts function to strip a live cartridge from a magazine at the firearm receiver, drive the stripped cartridge into the breech end of a firearm barrel, lock to the barrel breech, support the cartridge head during firing, and extract the spent brass of the cartridge from the breech end of the barrel after firing for ejection. Generally such bolts find application in both semi-automatic and fully automatic operations of these firearms.
In firearms such as the AR-15, AR-10, M-16 and variant platforms, such bolts are carried, for example, by a bolt carrier. The bolts are operationally connected to the carriers via a bolt cam pin extending through a cam slot in the carrier and into a transverse cam pin through-bore in the bolt. The lower end of the transverse open bore may have small staked projections limiting further passage of the cam pin, but the transverse bore extends through the bolt. Forces acting on the carrier serve to rotate the bolt, through the action of the cam pin in the cam slot, in one direction for loading and locking and in an opposite direction for unloading or extraction and consequent brass ejections. Such structure and operation is detailed in Stoner U.S. Pat. No. 2,951,424 and Larue U.S. Pat. No. 8,991,295, both of which are expressly incorporated herein as background by this express reference as if fully expressed in writing herein.
In some instances such as in high use, i.e. high round count, firearms, in firearms shooting heavy loads, in firearms where bolt materials are insufficiently strong, or are defective, in firearms where manufacturing tolerances are of wider range than desired, or in firearms exhibiting other aberrations, such prior bolts are attended by structural weaknesses, particularly in the bolt walls extending beside and around the open-ended cam pin bore through the bolt. The weaker bolt walls around the cam pin bore and between the bore openings thus constitute a weaker area in the bolt where the bolt may split, crack or disintegrate adversely affecting further action of the firearm. Failure of the firearm can be catastrophic to the user particularly when in an engagement in a military, law enforcement or defensive circumstance. While various manufacturing processes have been used to treat (peening) or to inspect (magnetic flux or particle processes) prior bolts, such prior bolts are still subject to failure proximate the open cam pin bore.
It has thus been one objective of this invention to provide an improved bolt structure for a firearm.
Another objective of the invention has been to provide a firearm bolt for AR-15, AR-10, M-16 and variant firearms with less propensity for breakage than that of prior bolts.
A yet further objective of the invention has been to provide an improved bolt having a cam pin bore therein, but without being subject to functional bolt weakness at the bore.
A still further objective of the invention has been to provide an improved bolt and cam pin combination.